1. Technical Field
The subject matter described herein generally relates to techniques for controlling the processing of audio signals to be played back by an audio device. In particular, the subject matter described herein relates to techniques for controlling the addition of sidetone to an audio signal to be played back by a telephony device and controlling the application of multi-channel decorrelation to audio signals to be played back by an audio device.
2. Description of Related Art
In audio communication systems, such as telephony systems, a speech signal captured by a remote or “far-end” telephony device is transmitted to a local or “near-end” telephony device and played back over one or more loudspeakers. At the near-end, the speech signal may be referred to as the “receive signal.” For a variety of reasons, the receive signal may be processed prior to playback.
For example, sidetone may be generated and added to the receive signal prior to playback thereof. Sidetone is a deliberate feedback of a near-end speaker's own speech signal (which may be referred to as the “send signal”) into the path of the receive signal. The presence of sidetone indicates an active telephone connection. When a telephony device is operated in a handset mode or when the receive signal is played back over a headset or a pair of headphones that have been connected to the telephony device, it is typically considered desirable to have sidetone. However, when the telephony device is operated in a hands-free mode or when the receive signal is played back over one or more external powered loudspeakers, sidetone is typically considered undesirable due to the possibility of acoustic echo.
As another example, when the receive signal comprises a multi-channel signal (e.g., a stereo signal having left and right channels), multi-channel decorrelation may be applied to the different channels prior to playback thereof. Multi-channel decorrelation is intended to help a multi-channel acoustic echo canceller distinguish between the different channels for the purposes of performing acoustic echo cancellation. Multi-channel decorrelation reduces the degree to which the different channels of the multi-channel receive signal are correlated by introducing a distortion (e.g., non-linearities) thereto. When a telephony device is operated in a handset mode or when the multi-channel receive signal is played back over a headset or a pair of headphones that have been connected to the telephony device, it may be deemed undesirable to apply multi-channel decorrelation, since acoustic echo may not be an issue. In such a case, there may be no reason to consume processing resources applying the technique. Furthermore, in such a case, there may be no reason to intentionally introduce a distortion into the receive signal as it may be noticeable by a user. However, when the telephony device is operated in a hands-free mode or when the receive signal is played back over one or more external powered loudspeakers, the application of multi-channel decorrelation may be considered desirable due to the possibility of acoustic echo.
A telephony device may not be capable of determining the type of device that is currently being used to play back the receive signal. This may be true, for example, when a user connects external powered speakers or a headset or headphones to the telephony device. If the telephony device is not capable of determining the type of speaker to which it is connected, then it may not be able to determine what type of receive signal processing may be appropriate for the type of speaker that is being used. This may result in, for example, sidetone being added to the receive signal when it is not desired or multi-channel decorrelation being applied to the receive signal when it is not beneficial or potentially harmful from an audio quality standpoint to do so.
The subject matter of the present application will now be described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.